Finned tube and method of making the same



Nov. 7, 1961 H. s. WOODRUFF FINNED TUBE AND METHOD OF MAKING THE SAME Filed April 22, 1958 mfl m b Q M m 9 5 .T a m i m I Y Q .H 7 [I11 N ad. l g 5252. w m fl r N N L. M M w O O m\ Q w 1 LHSL INVENTOR flea Pr S. h/aovEw-v' TTORNEYS United rates.

This invention has to do with finned tube such as is used, among other things, for base-board radiators and its general object is to provide an improved product and method of making the same.

It has been found that the heat output rating of finned tube can be very substantially increased by using a tube having a suitably roughened interior surface, as distinguished from the usual smooth bore.

It has also been found that a highly effective roughened surface can be achieved economically as an incident of or coincidentally with the expanding of the tube to secure the fins to it.

The invention will be readily understood from the fo lowing description of the accompanying drawings illustrating a preferred embodiment. In these drawings:

FIG. 1 is a broken-out, schematic illustration of the apparatus for practicing the method;

FIG. 2 is an enlarged, longitudinal section of a portion of a tube and a suitable expander, the section being on the line 2-2 of FIG. 3; and

FIG. 3 is a similarly enlarged cross-section on the line 3-3 of FIG. 2.

As usual, the components of the end product consist essentially of a metal tube 1 and metal fin elements 2 of any preferred shape. In general, the fin elements are stamped sheets, centrally apertured and sometimes provided with integral flanges 3 surrounding their central apertures. In any event, the fin apertures are so dimensioned that the elements can he slid on to the tube. The fins may be spaced from one another by the flanges or otherwise temporarily held in spaced relation by known methods. The fin elements are then secured to the tube by expanding the latter to cause them to grip it firmly.

While the desired roughened or uneven surface can be imparted to the tube in various ways, the preferred method is by what amounts to an internal ball peening operation Which serves the dual purpose of simultaneously expanding the tube and incorporating in its inner surface a multitude of closely spaced indentations.

This method can readily be accomplished by means of an expander which, in the preferred form illustrated, consists of a head unit adapted to be simultaneously rotated and drawn or forced through the tube. As shown, the head unit, mounted on the end of a rod or draw bar 4, consists of a cage 5 located between flanges 6, 7. The cage serves to locate a number of peen members, such as hardened steel balls 8 or the like (three equally spaced, in this instance). Within the cage and locked to the rod 4 against rotation relatively to it is a hammer member, consisting of a steel bar 9 of hexagonal section (FIG. 3). As will be understood, these elements are so dimensioned that the flats on the hammer permit the balls to enter the cage far enough to enable the entire head atent ice to be telescoped into the tube to be treated, while the corners of the hammer cause the balls to protrude and strike the tube.

As shown in the FIG. 1 diagram, the tube 1 with fin elements 2 on it is clamped at one end, as to post 10. As above mentioned, the tin elements are suitably positioned and temporarily held against longitudinal movement on the tube. The expander is shown coupled to a motor ll mounted on a carriage 1.2, a cable 13 and depending weight 14 serving to illustrate one way of drawing the expander through the tube.

The expander is inserted in the tube and the motor started. With the hammer rotating at relatively high speed, say, of the order of 3500 rpm, the interior of the tube is rapidly hammered by the balls being forced outwardly by the corners of the hammer.

The cage 5, it will be noted, is free to rotate and the intermittent striking of the balls by the hammer causes it to move, at slower speed, in the same direction as the hammer. In the result, as the expander is drawn through the tube, virtually its entire interior surface is covered with a multitude of closely spaced indentations as indicated at 15 in FIG. 2. Being of a relatively soft material (frequently copper) the tube is thereby expanded, so that the fin elements become securely locked to it.

Due to the simultaneous rotation and axial movement of the cage and balls, the resulting indenting of the tube interior exhibits a spiral pattern, this form of roughening the surface having proved to be especially eifective in disturbing the otherwise smooth flow of water through the tube' As will be recognized, the herein exemplified principles of the invention can be variously applied and, in the light of the foregoing illustrative description, the following is claimed:

The method of making a finned tube which comprises assembling a series of apertured fin elements on and in. sliding engagement with the outer surface of a tube, maintaining said fin elements in spaced positions relative to one another and progressively and simultaneously subjecting the interior of the tube to a series of ball peenings along closely spaced helical paths throughout the length thereof, said ball peenings coincidentally forcing the outer surface of the tube into tight fitting engagement with the fin elements and imparting a series of deformations following closely spaced helical paths in the interior surf-ace of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,606,336 Black Nov. 9, 1926 1,774,231 Harnsberger Aug. 26, 1930 1,998,047 Farr Apr. 16, 1935 2,004,389 7 Jones June 11, 1935 2,227,680 Townsend at al. J an. 7, 1941 2,377,406 Dedrick June 5, 1945 2,426,044 OBrien Aug. 19, 1947 2,442,009 Kline May 25, 1948 2,847,757 Mock et a1 Aug. 19, 1958 

